Wells with pervious lining

When the sub-soil is formed of gravel or coarse sand deposits, wells with pervious lining are considered suitable. This is because the gravel or coarse sand deposits have high permeability, allowing water to flow through them easily. In this context, a pervious lining refers to a lining material that allows water to pass through it.

Advantages of wells with pervious lining
- Increased water yield: The use of a pervious lining allows water to flow freely into the well from the surrounding gravel or coarse sand deposits. This results in a higher water yield compared to unlined wells.
- Reduced risk of clogging: Gravel or coarse sand deposits are prone to clogging due to the presence of fine particles. By using a pervious lining, the ingress of fine particles into the well can be minimized, reducing the risk of clogging.
- Better water quality: Pervious lining can act as a filter, preventing the entry of debris and contaminants into the well. This helps in maintaining better water quality.

Types of pervious lining
- Gravel packing: In this method, a layer of coarse gravel is packed around the well casing. The gravel acts as a filter, allowing water to pass through while retaining the surrounding soil and preventing clogging.
- Perforated pipe: Another method involves using a perforated pipe as the lining material. The pipe is wrapped in a geotextile fabric to prevent the ingress of fine particles while allowing water to flow through the perforations.

Considerations
- Design and installation: When constructing wells with pervious lining, it is important to consider the design and installation details. The size and spacing of perforations or the thickness of gravel packing should be carefully determined to optimize the water yield and prevent clogging.
- Maintenance: Regular maintenance is required to ensure the proper functioning of wells with pervious lining. This may involve periodic cleaning or replacement of the lining material to prevent clogging and maintain water quality.

In conclusion, when the sub-soil is formed of gravel or coarse sand deposits, wells with pervious lining are suitable. The use of a pervious lining increases water yield, reduces the risk of clogging, and improves water quality. Gravel packing and perforated pipes are common methods used for lining such wells. Proper design, installation, and maintenance are essential for the effective functioning of these wells.